Indicia applied permanently to articles of clothing and other textiles have become very popular. Fanciful indicia, such as logos, slogans, college names, sports team names and sayings, are now commonplace. As a result, screen printing has become very popular. Large, commercial operations screen printing textiles are common today.
Indicia can be one or more colors. Typically, a screen printing machine has at least one station for each color employed. For example, a design incorporating two colors will have at least two printing stations, one for each color. A design employing eight colors will have at least eight stations. Each station generally includes a printing head, which supports a single screen, the ink to be used at that station and a mechanism for applying the ink to the textile. Each color is carried by a single screen. The textile to be screened travels from printing station to printing station by one of a number of methods, such as a chain or a rigid arm. The textile is usually carried by a metal pallet, pallet support, flat bed, or platen. Common printing machines include turret, oval and linear. In addition to printing stations, there may also be curing stations to heat and set the inks placed on the textile or substrate.
Because of the intricacies and the numerous colors involved in more recent designs, registration and indexing of the textiles from station to station have become crucial requiring exacting tolerances. Accordingly, attention is mandatory to these aspects of the screen printing process.
Registration and complete accuracy are further demanded in the process leading up to printing the final product. Immediately following is a brief summary of this process.
First, the artwork is set up. The artwork, in the form of a film positive, is secured on a layout board. This layout board may have outwardly projecting, permanent perimeter pins (or a pin register bar). Next, a carrier sheet (optically clear polyester film) with prepunched perimeter holes is placed on the layout board with the prepunched perimeter holes being aligned with the perimeter pins of the layout board. An individual separates the colors by transferring the artwork by hand to one or more carrier sheets. In this separation/transference process, each carrier sheet represents a separate color to be used in the final screened textile. Thus, if there are six (6) colors being screened, there will be six (6) carrier sheets (Art Separations) completed.
Second, the screens are made. A vacuum exposure unit has basically three elements, that being a light/vacuum source, a cover, and a table disposed therebetween. Each carrier sheet is aligned with a blank screen, the cover is closed, and the screen/carrier sheet combination is subjected to vacuum and light. The result is a printing screen. The screen has interstices in the places where ink of a particular color is to be deposited onto the textile. As noted previously, for each color a different stencilled screen is used.
Third, each printing screen is secured to a printing head. Ink is then placed into the printing heads.
The textiles, one at a time, are loaded onto the travelling pallets and the pallets travel to each of the printing stations. The ink is applied to each textile through the screen at each station. Each textile is cured and the ink permitted to set.
In an effort to continuously improve upon the screening/printing process and machines available in the marketplace, the following advancements and improvements were developed to the apparatus and method of registering printing screens.